1. Field of the Invention
This invention relates to a method and circuit for liquid crystal display (LCD) panel flicker reduction, particularly to an adjustment circuit to be added to an LCD panel, thus reducing LCD panel flicker.
2. Description of the Related Art
In recent years, LCDs are increasingly popular due to smaller space requirement and lower power consumption. Large-size and high resolution LCDs are replacing conventional displays such as cathode ray tube (CRT) displays. However, such LCDs generally have flicker on the panels, which becomes more severe when the size of the LCD increases.
An LCD generally uses AC driving because electrical breakdown is caused by long-term bias voltage being applied. The AC driving means that data is changed between positive and negative regions. A diagram of inversion driving types of a typical LCD is shown in FIG. 1a. In FIG. 1a, symbol “+” is positive driving and symbol “−” is negative driving. AC driving of an LCD can be divided into frame inversion, row inversion, column inversion and dot inversion. Additionally, scan signal potential has two types. For example, the tri-state of scan line potential is high potential Vhigh, low potential Vlow and compensation potential Vgc, where Vhigh>Vlow>Vgc.
A schematic diagram of a typical LCD1 is shown in FIG. 1b. In FIG. 1b, the LCD includes a gate driver 10, a data driver 22 and an LCD panel. The LCD panel includes interlaced data lines and scan lines, which control display units. If one terminal of a display unit is connected to a common voltage source with common voltage level Vcom, such a structure is referred as a capacitance coupling on common (Cs on Common) structure. If the one terminal of the display unit is connected to another scan line providing the voltage level, such a structure is referred as a capacitance coupling on gate (Cs on Gate) structure. LCD 1 as show in FIG. 1b has the Cs on Gate structure. For example, the data line 18a and the scan line 20b control a display unit or unit 13, which includes a transistor 12ba, a capacitor 14ba and a liquid crystal unit 16ba. Gate and drain of the transistor 12ba are respectively connected to the scan line 20b and the data line 18a to control transistor 12ba on/off by means of scan signal on the scan line 20b in order to write data signal on the data line 18a in the devices 14ba and 16ba of the unit 13. Data signal is stored in capacitor in voltage level to drive the liquid crystal unit 16ba. Another terminal of the capacitor 14ba is connected to the scan line 20a. When the scan line 20b is enabled, the scan line 20a thus presents a voltage level. The scan driver 10 sequentially outputs scan signals on the scan lines 20a, 20b, . . . , 20m, such that transistors in a row of display units are instantly turned on and transistors in other rows are turned off. When the transistors are turned on, the data driver 22 outputs corresponding data signals to the row of display units through the data lines 18a, 18b, . . . , 18n according to image data to be displayed. Accordingly, repeating the above scan and output operations can complete the desired image display. However, every scan line is a wire with impedance and connects a plurality of capacitors through a plurality of transistors.
Therefore, as known to people skilled in the art, scan signal will be affected by RC effect so as to change the waveform. For example, a scan signal on scan line 20b turns transistor 12ba on/off using a normal wave but turns transistor 12bn on/off using a deformed wave due to the RC effect. Both normal and deformed waves can offer a similar function but may cause an error in the deformed waveform. For example, the on/off may result in capacitor 16ba experiencing a correct data signal but capacitor 16bn experiencing an incorrect data signal. Further, the correct and incorrect data signals cause brightness or chromatic difference on an LCD which causes perceived flicker for views due to positive and negative cycle changes. The flicker intensifies with larger LCDs at higher operating frequencies.
Consequently, there is a need to develop new method and devices for LCD panel flicker reduction.